Patent GB-593807-A (GB)
Title: Improvement in liquid level indicators
IPC: G01F23/16
Filed: 1945-01-26
Abstract: 593,807. Indicating liquid-levels. COTTRELL, H. L. (Wallace & Tiernan Products, Inc.). Jan. 26, 1945, No. 2105. [A Specification was laid open to inspection under Sect. 91 of the Acts, July 7, 1945.] [Class 123 (i)] [Also in Groups XIX, XXVIII and XXXV] Apparatus, shown diagrammatically in Fig. 15, for measuring the level of liquid in a tank D comprises a casing 10 provided with a sealed chamber 11, in which is mounted a pressure gauge 20 ... 27, and a second chamber 12 which locates an electrically driven air pump 13 from the pressure end of which tubes 30, 44 extend to fittings 31, 41, the fitting 31 communicating with pressure tubes 32. 33 for connecting the pressure-responsive element 20 of the gauge to a zero point near the bottom of the tank D and the fitting 41 with pressureequilizing tubes 40, 42 for connecting the chamber 11 to the space in the said tank D above the liquid level. The pump chamber 12 is provided with a filter-protected opening 15 for admitting air to the suction inlet 16 of the pump, and, when the apparatus is applied to a sealed tank, a further pressure-equalizing tube 48 leading. from the space above the liquid is connected to said opening. The arrangement is such that, with the pump 13 in operation, an air pressure is built-up sufficient to permit air to escape from the end of the tube 32, and the difference between this pressure and the pressure in the tank above the liquid, which is indicated by the gauge pointer 27, is a measure of the liquid level. In the application of the invention to the fuel-tank of an aircraft, the casing 10 is mounted on the instrument board thereof and the tubes 32, 40 lead to nipples 109, 110 in the respective sealed halves of a box device B, Fig. 10, the base 105a of which is secured in an opening in the top wall of the tank D and is fitted with a pair of spring-pressed valves 122 which control openings in base fittings 120. The fittings 120 associated with the nipple 109 and tube 32 is provided with a tube 116 extending downward to near the bottom of the tank D, and both fittings include weighted balls 130 which normally retain the valves 122 in an open position but permit them to close and prevent entrance of liquid to the box B should the tank tilt. The balls have guiding rods 131, and tubes 132 limit lifting movement thereof. In a modification the normally open valves are in the form of discs of cork which are located in small chambers in the base 105a of the box B and are moved by the liquid itself to close the valves to prevent entrance of liquid to the said box. The pump, Fig. 6, comprises a cylinder 90 with a piston 97 reciprocated by a rod 98 coupled by an arm 142 to a vibratory armature 141 of an electromagnetic motor 14. The cylinder 90 opens into a suction chamber 92 which has the air inlet 16, fitted with a non-return valve 94, and communicates with a pressure chamber 93, from which the tubes 32, 40 lead, by a port 95 through a non-return valve 96. The electromagnet 140 of the motor is supplied with current from a fitting 155 under the control of a make-and-break device actuated by movement of the armature 141, said device comprising a fixed contact 150, which is mounted on but insulated from the pole piece 144 of the magnet, and a movable contact 152 at the end of a flat rod 153 of magnetic material which is pivotally connected by a thin spring plate 154 to the pole piece 143. A bar 156 extends between the armature 141 and rod 153, said bar being pivoted to the armature and having a lost-motion connection with the rod 153 in the form of a stud 157 on the rod 153 extending through a slot 158 in said bar, the arrangement being such that, during the first part of the inward movement of the armature, the rod 153 is held in its circuitclosing position by the magnet until the end of the slot 158 engages the stud 157, when continued movement of the armature separates the contacts to break the magnet circuit. Current is supplied to the magnet coil by wires a, b, which lead, the wire a to the contact 151 and thence through the contacts and the rod 153 to a pole piece 143 and the magnet core, and the wire b to one end of the coil the other end of which is connected to the core. The pressure gauge, Fig. 5, comprises the capsule 20 of conventional form one side of which is rigidly connected to a bracket 21 and from the other side of which extends an operating rod 22 pivotally connected through a flexible portion 76 thereof to a lever 23, the latter having a flexible mounting 75 and carrying a gear segment 24 which engages a pinion 25 on the spindle 26 of the gauge pointer 27. The connection between the rod 22 and lever 23 is adjustable so that the movement of the pointer for a given expansion or contraction of the capsule 20 may be varied, and in order to prevent back-lash between the segment 24 and pinion 25 the lever 23 is provided with a light spring 80 from which a fine wire 81 extends to and is secured around a pulley 82 on the pointer spindle 26. A light spring 83, connected at one end to a thimble 66 on the capsule 20 and at the other end to an adjustable lever 84, is also provided for setting the pointer 27 in its zero position, and the capsule may have an associated stop 85 for limiting the expanding movement thereof.